/**
  * Author: Mei
  * Date: 2020-11-21 9:07
  * Description: 
  *
  */
#include <iostream>

using namespace std;

template <typename T, typename R>
//R add(T a, T b) {
//    return a + b;
//}
auto add(T a, R b)-> decltype(a*b) {
    return a * b;
}
int main() {
    int a = 10; double b = 20;
    cout << add(a, b);

    return 0;
}